In large scale manufacturing and assembly plants, such as those used in automobile manufacturing, hundreds of stations consisting of a plurality of machines may work simultaneously. In a large production environment, the production line may include miles of conveyors. Work in progress includes but is not limited to units of production, pallets, carriers, product and parts. A station may include a single or a plurality of machines. In an assembly plant, a station may be unmanned or include a staff operator.
A buffer is a storage area such as a conveyor, transport (i.e. forklift, cart, truck, etc.) silo between stations, or simply a place on the floor. An upstream buffer and a downstream buffer generally can hold parts in excess of standard in-process stock. If a buffer is empty, the station drawing from that buffer is starved. If a buffer is full, the station feeding that buffer will be blocked.
In a manufacturing, assembly, production, or any other type of plant, processes for operation of the machines are preplanned by process and plant engineers. During set up for production, processing for assembly operations breaks down the production process into components and assigns tasks to individual robots or machines. Machines such as welding machines are configured to operate in multiple dimensions and are programmable to weld specific spots on a product. Other machines, including stud weld or adhesive dispense machines are also configured in a similar fashion.
Once the plant process is determined, the weld robots, in particular, are manually assigned to a rigid set of weld sequences. In the event that ambient conditions change, that is, a machine or station is taken off line for reasons of malfunction or others, production may stop. In the event that there is a machine stoppage, manually rerouting product to a machine programmed to operate in the same manner as the stopped machine will allow production to continue.
Manually reallocating work from a halted machine or station to an operational station requires many physical steps and time. However, oftentimes, manual rerouting does not take place and the line will not start moving again until the stopped machine is restarted. In either event, buffers upstream become blocked and buffers downstream become starved. In the event that adjustments in production are needed, reassignment to balance workloads, accommodate product changes, or respond to individual equipment downtime conditions is accomplished manually.